Image processing apparatus and method thereof

ABSTRACT

The present invention relates to an image processing method and apparatus for processing compressed image generated by segmenting image data into a plurality of MCUs and using a compression method in which a frequency transformation is applied to each MCU. In a case that the compressed image is decoded, each MCU is classified according to the frequency coefficients therein, and color separated data is generated for each MCU based on the decoded data resulting from the decoding and the results of the MCU classification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus andmethod for processing image data compressed using a frequencytransformation such as a DCT (Discrete Cosine Transform).

2. Description of the Related Art

In recent years, as the use of digital cameras has become widespread,printing digital camera-captured image data using printers has becomemore common. As a result, various printing methods have appeared,including direct-from-camera printing in which the digital camera isdirectly connected to the printer and memory card printing in which amemory card of a digital camera is attached to a printer and the imagedata stored therein is printed. In these technologies, the printerreceives image data from the digital camera or memory card, decodes theimage data to generate print data, and prints.

Since the resources (calculation power of CPU, memory capacity) ofprinters which process image data in this way are much more limited incomparison to the resources of PCs, the ability to perform theprocessing to generate print data efficiently is a requirement forsystems which perform direct printing.

Aside from this trend for direct printing, the advancement of digitalcamera technology has accelerated, and the number of pixels in digitalcamera imaging has increased sharply. To suppress the size of the imagedata without loss of image quality, image data is processed using acolor image compression format based on the DCT when saved on the memorycard. The standard example among these formats is JPEG. In JPEG, theimage data is divided into a plurality of blocks called MCUs (MinimumCoded Units), and each MCU undergoes DCT conversion. A high degree ofcompression is then realized by making use of the low sensitivity tohigh frequency signals which characterizes human vision and eliminatingthe high-frequency components in the DCT coefficients (frequencycoefficients). However, encoding to and decoding from the JPEG formatimparts a large processing load.

As a technique for increasing the efficiency of processing which makesuse of JPEG characteristics, Japanese Patent Laid-Open No. 2001-145107proposes a technique for increasing the speed of baseline JPEGcompression processing by taking frequency characteristics of the MCUinto consideration. In this technique, the image data is divided intoMCUs, the MCUs are classified into uniform color MCU and non-uniformcolor MCUs. The uniform color MCUs are then encoded by finding only DCcoefficients using a simple calculation, and the non-uniform color MCUsare encoded normally. Thus, techniques of this type for reducing theload of encoding and decoding by paying close attention to thecharacteristics of the DCT used in JPEG have already been proposed.However, these techniques are limited to the efficient treatment of MCUsof uniform color.

Besides decoding the JPEG coded image data or the like, the printer mustalso generate print data which can be printed by the printer from thedecoded color image data. The following describes a technique forefficiently generating print data from the decoded color image data.

Generally, color image data is expressed using a color space, in such asCRT, which differs from the color space of a printer. Due to thediversity of color spaces for expressing color image data, after a firstconversion into a standard color space it is necessary to resolve thedata into the colors of the printer-specific coloring materials. Sincean enormous amount of processing is required to generate the color datafor the printer-specific coloring materials, techniques for efficientlyperforming this processing have been proposed.

Japanese Patent Laid-Open No. 2005-53009 proposes a technique forsuppressing the processing speed reduction resulting from color spaceconversion in performing color conversion process, color correction andprint processing with colors conversion. In this technique, input dataare stored in correspondence with device-dependent data, and the storeddata are used as a color processing cache. The cache region isstructured to allow storage of a plurality of items of cache data, and acache data table is searched to judge whether the input data and colorprocessing result for given input data has already been cached incombination. When the combination has been cached in the cache datatable, the cached data can be used and the color processing of the inputdata can be omitted. When the combination has not been cached in thecache data table, color processing is implemented on the input data, andthe result is stored in an empty region of the cache region or writtenover a region that is in use. This process allows a reduction in theamount of processing required for the color processing. Moreover, as theamount of cached data increases, the cache hit rate generally increases.

However, the above-described technique has the following disadvantage.Since it is necessary to store a plurality of items of cache data in thecache data table, the cost of the cache region increases with the sizeof the table. Also, as the size of the table increases, there is acorresponding increase in the amount of time taken to search the table.

Thus, although techniques have been already proposed for reducing theprocessing load for particular image formats frequently used by printerand for improving the efficiency of color processing when generatingprint data from the image data, there is still room for improvement.

SUMMARY OF THE INVENTION

An aspect of the present invention is to eliminate the above-mentionedconventional problems.

A feature of the present invention is to further accelerate the colorprocessing for color image data compressed using a frequencytransformation, such as DCT.

According to the present invention, there is provided an imageprocessing apparatus for processing compressed image data generated bysegmenting image data into blocks and using a compression method whichapplies a frequency transformation to each block, the image processingapparatus comprising:

a decoder configured to decode the compressed image data and outputdecoded data;

a block classification unit configured to classify blocks according tofrequency coefficients in the blocks decoded by the decoder; and

a color separated data generator configured to generate color separateddata in block units based on the decoded data decoded by the decoder anda result of classification by the block classification unit.

According to the present invention, there is provided an imageprocessing method for processing inputted compressed image datagenerated by segmenting image data into blocks and using a compressionmethod to apply a frequency transformation to each block, the imageprocessing method comprising the steps of:

decoding the compressed image and outputting decoded data;

classifying blocks according to frequency coefficients in the blocksdecoded in the decoding step; and

generating color separated data in block units based on the decoded dataand a result of classification in the classifying step.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram showing a schematic construction of the printsystem (image processing system) common to the exemplary embodiments ofthe present invention;

FIG. 2 is a block diagram showing a schematic of hardware for an imageprocessing apparatus that forms the print system of the exemplaryembodiments;

FIG. 3 shows a modular construction of software used for the printfunction of the image processing apparatus of the exemplary embodiments;

FIG. 4 is a flowchart describing processing for generating print data bya data conversion module of the exemplary embodiments;

FIG. 5 is a block diagram explaining color space conversion processingof the exemplary embodiments.

FIG. 6A to FIG. 6E depict views illustrating DCT coefficients obtainedusing an inverse quantization unit of the exemplary embodiments;

FIG. 7A to FIG. 7D depict views illustrating pixel values obtained usingan IDCT;

FIG. 8 is a flowchart describing processing executed by a colorseparated data generator of a first exemplary embodiment of the presentinvention;

FIG. 9 is a flowchart describing generation processing 1 of colorseparated data corresponding to an MCU of “pattern A” of the firstexemplary embodiment;

FIG. 10 is a flowchart describing generation processing 2 of colorseparated data corresponding to an MCU of “pattern B” of the firstexemplary embodiment;

FIG. 11 is a flowchart describing generation processing 3 of colorseparated data corresponding to an MCU of “pattern C” of the firstexemplary embodiment;

FIG. 12 is a flowchart describing generation processing 4 of colorseparated data corresponding to an MCU of “pattern D” of the firstexemplary embodiment;

FIG. 13 is a block diagram explaining another example of color spaceconversion processing of the first exemplary embodiment of the presentinvention;

FIG. 14 is a block diagram explaining color space conversion processingof a second exemplary embodiment of the present invention;

FIG. 15 is a flow chart describing processing executed by the resizedcolor separated data generator of the image processing apparatus of thesecond exemplary embodiment of the present invention;

FIG. 16 is a flowchart describing generation processing 1 of resizedcolor separated data corresponding to an MCU of “pattern A” of thesecond exemplary embodiment;

FIG. 17 is a flowchart describing generation processing 2 of resizedcolor separated data corresponding to an MCU “pattern B” of the secondexemplary embodiment;

FIG. 18 is a flowchart describing generation processing 3 of resizedcolor separated data corresponding to an MCU “pattern C” of the secondexemplary embodiment; and

FIG. 19 is a flowchart describing generation processing 4 of resizedcolor separated data corresponding to an MCU “pattern D” of the secondexemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Numerous embodiments of the present invention will now herein bedescribed below in detail with reference to the accompanying drawings.The following embodiments are not intended to limit the claims of thepresent invention and not all combinations of features described in theembodiments are essential to the solving means of the present invention.Note that hereinafter for the sake of convenience, the function of aprinter generating print data based on received image data andsubsequently printing will be referred to as “direct printing”.

First, an overall concept of an image processing system, a hardwareconstruction concept, and a software construction concept common to thefollowing exemplary embodiments are described.

FIG. 1 is a block diagram showing a schematic construction of a printsystem (image processing system) common to the exemplary embodiments ofthe present invention.

The print system includes a host apparatus 11 that is a PC or the likeand an image processing apparatus 12 that is a printer or the like,connected via a bidirectional interface 13.

The following describes the concept of the hardware construction of theimage processing apparatus 12.

FIG. 2 is a block diagram showing a schematic construction of hardwareof the image processing apparatus 12 that forms the print system of theexemplary embodiments.

As shown in FIG. 2, reference numeral 1000 denotes a control board. ASIC1001 includes an interfacing unit (not shown in the drawings) forcontrolling the interface of various units which connect to the ASIC1001, and a CPU 1001 a for executing various processing, such as imagedata generation and the like. A connector 1002 connects the controlboard 1000 and a console unit 1003. Using the console unit 1003, a useris able to perform operations such as setting various print settinginformation, looking at and specifying images stored in a memory card(MC) 1007, specifying the start of printing, cancelling the printing,and the like. A connector 1004 connects the console unit 1003 and aviewer 1005. The viewer 1005 displays images stored in the memory card1007, GUI menus, various error messages, and the like. A connector 1006connects the memory card 1007 and the control board 1000, and the ASIC1001 is capable of directly reading image data from the memory card 1007and printing.

A DSC USB bus connector 1008 is a USB bus connector for connecting adigital camera (DSC) 1010 to the control board 1000, and a connector1009 is for connecting the digital camera 1010. The digital camera 1010is constructed to allow output of image data and print settinginformation stored in the internal memory to the image processingapparatus 12. Note that various constructions may be employed for thedigital camera 1010. For instance, a memory may be included as aninternal unit or a slot for installing a removable memory may beprovided. This arrangement allows the image data in the digital camera1010 to be processed in accordance with the print setting informationset in the digital camera 1010, thereby enabling the direct printing.

A USB bus hub 1017 passes data from the PC 1013 connected via theconnector 1012 to the ASIC 1001 in a case that image data from the PC1013 is printed. A memory 1014 includes a program memory for storingcontrol programs and the like for the CPU 1001 a of the ASIC 1001. Alsoincluded are a RAM area for storing programs during execution, and awork memory area for storing data such as image data, print settinginformation and various later-described flags and variables.

A connector 1015 connects a CR (carriage) control board and a print head1016 to the control board 1000. Reference numeral 1017 denotes a LF(line feed) motor driver, a reference numeral 1018 denotes a connectorthat connects a LF motor 1019 to the LF motor driver 1017. In the sameway, reference numeral 1020 denotes an ASF (auto sheet feed) motordriver, and reference numeral 1021 denotes a connector connecting theASF motor 1022 to the ASF motor driver 1020. A DC voltage is inputted bya power supply unit 1024 via a power connector 1023. The power supplyunit 1024 may be an AC adaptor for generating a DC voltage from abattery or commercial power supply.

The following describes the concept of the software construction of theimage processing apparatus 12 of the exemplary embodiments. Here, theprint function is described.

FIG. 3 shows a modular construction of software used for the printfunction of the image processing apparatus 12 of the exemplaryembodiments. The following describes the print processing with referenceto FIG. 3. Note that in the cases described here, the image data is readfrom the memory card 1007 and printed, the data is received from the PC1013 and printed, or the data is received from the digital camera 1010and printed. Note also that each module, rasteriser, and interfacecontrol module shown in FIG. 3 is realized by the CPU 1001 a using aprogram stored in the memory 1014.

First, the case in which the image data is inputted from the memory card1007 and printed is described.

A direct print function control module 2001 connects to a DSC I/F module2002, a memory card I/F module 2004, a PC USB I/F module 2017, andreceives information about the connection states of the DSC 1010, thememory card 1007, and the PC 1013, respectively. The information aboutthe connection states is sent via a console I/F module 2006 to theconsole unit 1003 and displayed by the console unit 1003. The directprint function control module 2001 judges whether a direct print betweenthe memory card 1007 or the digital camera 1010 and the control board1000 is currently possible and displays a user settings menu whichincludes settings which are specifiable by the user via the console unit1003. The console I/F module 2006 receives various print-relatedsettings such as paper settings irrespective of the connection states ofthe DSC 1010 and the memory card 1007, and stores current print settinginformation. A menu screen or the like for specifying the print settingmethod is displayed on the viewer 100S. The console I/F module 2006communicates with a viewer I/F module 2008, and supplies key operationinformation of the console unit 1003. The console I/F module 2006further supplies connection state information regarding the DSC 1010,the memory card 1007, and the PC 1013. Then, based on the suppliedinformation, menu screens showing available settings and image data fromthe connected device are displayed on the viewer 1005.

In a case that the memory card 1007 is connected, a user makes use ofthe console unit 1003 and the viewer 1005 to view image data stored inthe memory card 1007, specify the image data to be printed, and instructthat printing is to start. When the user is to print image data of thememory card 1007, pressing a print start key of the console unit 1003causes the console I/F module 2006 to issue a print start request to thedirect print function control module 2001. Upon receiving the printstart request, the direct print function control module 2001 notifies amain control module 2000 of the print start request. The direct printfunction control module 2001 instructs the DSC USB I/F module 2002 andthe PC USB I/F module 2017 to inhibit reception of data from the DSC1010 and the PC 1013, i.e. from components other than the memory card1007. When these instruction have been received and the system isentirely devoted to printing of the image data of the memory card 1007,the main control module 2000 permits the direct print function controlmodule 2001 to switch to direct print processing. On receiving thispermission, the direct print function control module 2001 gives a printinstruction to a rasterising manager 2010.

The rasterising manager 2010 selects a rasterising module appropriatefor current print mode and causes execution of raster processing. Forinstance, in a case that print data generated by the PC 1013 is to bereceived from the PC 1013 and printed, the data received from the PC1013 is itself the print data. In contrast, when image data from the DSC1010 or the memory card 1007 is to be printed, a rasterising module 2013has to generate print data. Hence, in a case that the generated printdata is to be received from the PC 1013 and printed, the rasterisingmanager 2010 selects a non-direct print rasterising module 2011 andcauses processing of the print data from the PC 1013. Further, in a casethat the image data from the DSC 1010 or memory card 1007 is to bereceived and printed, the rasterising manager 2010 causes processing bya job generation module 2012 and the rasterising module 2013.

The job generation module 2012 receives print processing instructionsfrom the rasterising manager 2010. The job generation module 2012 asksthe direct print function control module 2001 whether the direct printis a direct print from the memory card 1007 or a direct print from thedigital camera 1010. If notified that the direct print is a direct printfrom the memory card 1007, the job generation module 2012 acquires theprint setting information set by the user from the console I/F module2006, and generates a job. The job generation module 2012 gives a printprocessing instruction to the rasterising module 2013.

The rasterising module 2013 generates print data based on the jobinformation. This job information includes instructions about the papersize and type, and the type of printing method. Possible printingmethods include n-in-1 printing and index printing. The job informationfurther includes instructions relating to printing position and varioustypes of image correction, information relating to image files specifiedfor printing, and information indicating whether the direct printing isinstructed from the memory card 1007 or the digital camera 1010.

The rasterising module 2013 interprets the job information, determinesan operation mode of an engine unit based on a type of paper and printquality, and communicates information concerning the operation mode toan engine control module 2015. Then in accordance with the paper sizeand printing method, the rasterising module 2013 generates layoutinformation for determining the size of an image and a position in asheet and assigning the image to the position of the sheet, andgenerates print data using the information relating to the image filespecified for printing. A data conversion module 2014 converts the printdata generated by the rasterising module 2013 and the non-direct printrasterising module 2011 to a data format suitable for reception by theprinter engine unit.

FIG. 4 is a flowchart describing processing for generating print datausing the data conversion module 2014 of the exemplary embodiments. Notethat the program for executing this processing is stored in the memory1014 and executed under the control of the CPU 1001 a.

First, in step S1, the image file specified for printing is read anddecoded. Next, in step S2, the color space of the image data resultingfrom the decoding is converted to a color space specific to the imageprocessing apparatus 12. Next, in step S3, the image data is resized inaccordance with the layout information. Lastly, in step S4, pixel dataof the resized image data is quantized (half-toning). Note that thequantization depends on the format of the data processed by the imageprocessing apparatus 12. For instance, in a case that the imageprocessing apparatus 12 executes printing using binary data, the data isconverted to binary data. In a case that the image processing apparatusprints based on multivalued data (for printing using ink shading, orprinting using large and small dots), the data is converted tomultivalued data. The above describes the concept of the print datageneration procedure by the data conversion module 2014 of the exemplaryembodiment.

Further, the rasterising module 2013 issues, as required, requests suchas paper supply and discharge requests, feed requests, and printrequests to the engine control module 2015, and proceeds through theprocessing in synchronism with an operation of the engine controlmodule, while exchanging messages with the engine control module 2015.In a case of direct printing from the memory card 1007, the image filespecified for printing is accessed via the memory card I/F module 2004.Further, in a case of direct printing from the digital camera 1010, theimage file in the digital camera 1010 is accessed via the DSC USP I/Fmodule 2002.

The data conversion module 2014 converts print data generated by therasterising module 2013 or the non-direct print rasterising module 2011into data of a data format suitable for reception by the printer engineunit (not shown in the drawings) of the image processing apparatus 12.Then, whenever a predetermined amount of converted data has beenprepared, the data conversion module 2014 notifies the engine controlmodule 2015 via the main control module 2000. Taking into account theoperation mode of the printer engine unit, the engine control module2015 passed the data converted by the data conversion module 214 to theprinter engine unit, and causes the printer engine unit to perform printprocessing.

The following describes the processing in the case that image data isreceived from the digital camera 1010 and direct printing is performed.

The direct print function control module 2001 performs processing in asimilar manner to the direct printing in which image data is printedfrom the memory card 1007.

When the digital camera 1010 is connected, a user makes use of functionsprovided in the digital camera 1010 to look at images stored in a memoryunit of the digital camera 1010, specify the image for printing and theprint settings, and instruct that printing should begin. In the case ofdirect printing from the digital camera 1010, when a print start key ofthe digital camera 1010 is pressed, a print start request is issued tothe direct print function control module 2001 from the DSC USB I/Fmodule 2002. Upon receiving the print start request, the direct printfunction control module 2001 notifies the main control module 2000 ofthe print start request. The main control module 2000 instructs thememory card I/F module 2004 and the PC USB I/F module 2017 to inhibitreception of data from the memory card 1007 and the PC 1013, i.e. fromcomponents other than the digital camera 1010. When these instructionshave been received and the system is entirely devoted to printing imagedata from the digital camera 1010, the main control module 2000 permitsthe direct print function control module 2001 to switch to the directprint processing.

In this case, operations of the direct print function control module2001 are similar to the operations performed in the case of the directprint of image data from the memory card 1007.

The job generation module 2012 receives print processing instructionsfrom the rasterising manager 2010. The job generation module 2012 asksthe direct print function control module 2001 whether the direct printis a direct print of image data from the memory card 1007 or a directprint of image data from the digital camera 1010. If the resultindicates the direct print of image data from the digital camera 1010,the job generation module 2012 acquires the print setting informationset by the user via the DSC USB I/F module 2002 to generate a print job.The job generation module 2012 gives a print processing instruction tothe rasterising module 2013. The operations of the rasterising module2013 at this point are substantially the same as the operations in thedirect print of image data from the memory card 1007. The onlydifference is that, in the latter case, the desired image file isaccessed via the DSC USB I/F module 2002. Further, in the processing bythe data conversion module 2014 and the engine control module 2015, theoperations are similar to the operations performed in the direct printof image data from the memory card 1007. The above has described theconcept of the software construction.

The feature of the exemplary embodiments relates to the print datageneration processing executed by the rasterising module 2013 in FIG. 3.In particular, the feature relates to processing for decoding colorimage data that has been compressed using the DCT and converting thecolor space of the decoded image data to the color space specific to aparticular device.

The following describes a first exemplary embodiment, paying closeattention to the print data generation processing performed on the colorimage data compressed using the DOCT. For the sake of convenience, anexample is described in which the color image data compressed using theDCT is JPEG data.

First Embodiment

In the first embodiment, the object is to speedily generate colorseparated data resulting by the conversion from the JPEG data into thedevice-specific color space.

As described above with reference to FIG. 4, the color separated dataresulting by the conversion from the JPEG data into the device-specificcolor space is generated in accordance with the following steps.

(1) The specified image file is read and image data of the image file isdecoded.

(2) The color space of the decoded image data is converted into adevice-specific color space.

FIG. 5 is a block diagram explaining color space conversion processingof the exemplary embodiments. This processing corresponds to steps S1and S2 of in the flowchart of FIG. 4.

First, the JPEG data received from the memory card 1007, the digitalcamera 1010, or the PC 1013 is segmented into AC components and DCcomponents and Huffman decoded by a Huffman decoder 500. This allows thequantized DCT coefficient (quantized frequency coefficient) data foreach MCU to be obtained. Next, the quantized DCT coefficient dataoutputted from the Huffman decoder 500 undergoes inverse quantization byan inverse quantization unit 501 to obtain the DCT coefficient data foreach MCU. The DCT coefficient data for each MCU then undergoes inverseDCT conversion by an inverse DCT unit 502. The resulting output is thedecoded JPEG data. The color space of the decoded JPEG data is notlimited to a particular format. However, DCF (Design rule for CameraFile system) version 1.0, which is a camera file system guideline,indicates that the data format should be YCbCr. On this basis, here itis assumed that the decoded JPEG data is outputted as YCbCr data.

The DCT coefficient data for each MCU, which has been generated by theinverse quantization unit 501 is also simultaneously supplied to an MCUclassification data generator 503. The MCU classification data generator503 analyzes the DCT coefficient data, classifies the MCUs into fourcategories, and outputs MCU classification data.

The following describes the classification method with reference to FIG.6A to FIG. 6E and FIG. 7A to FIG. 7D.

FIG. 6A to FIG. 6E depict views illustrating DCT coefficients obtainedusing an inverse quantization unit of the exemplary embodiments. In thedrawings, “m” and “n” respectively represent horizontal frequencycomponents (m=0 to m=7) and the vertical frequency components (n=0 ton=7).

FIG. 7A to FIG. 7D depict views illustrating pixel values obtained usingthe IDCT unit 502, and “x” and “y” in the drawings designate pixelpositions in the MCU.

FIG. 6A shows a DCT coefficient block 600 in a given MCU, as generatedby the inverse quantization unit 501. Since the MCU is constructed froman 8×8 set of pixels, an 8×8 set of components is obtained for thecorresponding DCT coefficients.

Formula (1) below is the conversion formula used by the IDCT unit 502,and “m” and “n” in the formula correspond to the “m” and “n” in FIG. 6Ato FIG. 6E.

$\begin{matrix}{S_{x,y} = {\frac{1}{4}{\sum\limits_{m = 0}^{7}{\sum\limits_{n = 0}^{7}{C_{m}C_{n}S_{mn}\cos\frac{\left( {{2x} + 1} \right)m\;\pi}{16}\cos\frac{\left( {{2y} + 1} \right)n\;\pi}{16}}}}}} & \left\lbrack {{Formula}\mspace{20mu} 1} \right\rbrack\end{matrix}$C _(m) , C _(n)=(1/√2) (when m, n=0)C _(m) , C _(n)=1 (otherwise)

Here, C_(m) is the conversion coefficient for when the horizontalfrequency coefficient is “m”, and C_(n) is the conversion coefficientfor when the vertical frequency coefficient is “n”. Further, S_(mn) isthe frequency component value at the frequency component (m,n), andS_(xy) is the pixel value at the position (x,y) in the corresponding MCUobtained from the IDCT unit 502.

As is clear from the above-described formula (1), the coefficientindicated by reference numeral 601 in FIG. 6B, i.e. the coefficient for(m,n)=(0, 0), is the DC component. The coefficients indicated byreference numeral 602 in FIG. 6C, i.e. the group of coefficients forwhich n=0, have DC component and horizontal AC components. Similarly,the coefficients indicated by reference numeral 603 in FIG. 6D, i.e. thegroup of coefficients for which m=0, have a DC component and vertical ACcomponents. From the above it is possible to state the following.

If the DCT coefficients of a given MCU include only the DC component601, as shown in FIG. 6B, the MCU can be understood to have pixels whichare all of a single color, as shown in FIG. 7A. For the sake ofconvenience, in the following description, a data pattern composed ofpixels which are all of a single color, as shown in FIG. 7A, is referredto as “pattern A”.

If the DCT coefficients of a given MCU include a DC component andhorizontal AC components, as indicated by reference numeral 602 in FIG.6C, the given MCU can be understood to include a pattern of verticalstripes, as shown in FIG. 7B. In other words, any eight consecutivepixels in the y-direction in the MCU have the same pixel value. For thesake of convenience, in the following description, a data pattern inwhich any eight consecutive pixels in the y-direction have the samepixel value, as shown in FIG. 7B, is referred to as “pattern B”.

Moreover, if the DCT coefficients of a given MCU include a DC componentand vertical AC components, as indicated by reference numeral 603 inFIG. 6C, the given MCU can be understood to include a pattern ofhorizontal stripes, as shown in FIG. 7C. In other words, any eightconsecutive pixels in the x-direction in the MCU have the same pixelvalue. For the sake of convenience, in the following description, a datapattern in which any eight consecutive pixels in the x-direction havethe same pixel value, as shown in FIG. 7C, is referred to as “patternC”.

Lastly, if the data pattern does not correspond to any of the above, theMCU can be understood to have a mix of frequency components in thehorizontal and vertical directions as shown in FIG. 7D. In other words,there is no guarantee of continuity in the x-direction or they-direction. For the sake of convenience, in the following description,a data pattern without guaranteed continuity in the x-direction or they-direction is referred to as “pattern D”. By analyzing the DCTcoefficients in this way, it is possible to specify the pixel valuepattern of the MCU.

In this way, the MCU classification data generator 503 specifies thepixel value pattern of the MCU based on the distribution of the DCTcoefficients, and outputs the resulting data as MCU classification data520 to a color separated data generator 504.

FIG. 6E shows an example of the MCU classification data 520 generatedand outputted by the MCU classification data generator 503.

In this example, since the MCU is classified as being one of theabove-described four patterns (“pattern A” to “pattern D”), the MCUclassification data 520 consists of two bits per MCU. Thus, “1” isoutputted for MCUs of “pattern A”, “2” is outputted for MCUs of “patternB”, “3” is outputted for MCUs of “pattern C”, and, lastly, “0” isoutputted for “pattern D”. The above is a description relating to amethod for classifying the MCUs.

The MCU classification data 520 and the decoded JPEG data are theninputted into the color separated data generator 504.

The color separated data generator 504 includes a color space converter505 and a color separator 506. The color space converter 505 convertsthe color space of the inputted decoded JPEG data into a predefinedcolor space suitable for input to the color separator 506. Here, whenthe predefined color space is set to be sRGB, the YCbCr decoded JPEGdata is converted to sRGB in the color space converter 505 using amatrix operations or the like. Various techniques exist for convertingthe color space, but in the present embodiment there are no particularlimits on the technique employed.

The color separator 506 converts the inputted image data to thedevice-specific color space by further conversion processing using anLUT or the like, performs gradation correction where necessary, andoutputs the result. For instance, if the predefined color space is sRGBand a CMYK color space is set as the device-specific color space,inputted sRGB data is converted and outputted as CMYK data (colorseparated data). Note that the device-specific color space is notlimited to being the CMYK color space, and may be an RGB color space. Inthis case, the device-specific RGB color space must be converted to theCMYK color space. Various techniques exist for the color separationprocessing to convert to the device-specific color space, but in thepresent embodiment there are no particular limits on the techniqueemployed.

Using the color space converter 505 and the color separator 506, thecolor separated data generator 504 generates device-specific color spacedata from the inputted decoded JPEG data, and outputs the result. Atthis point, when the color space converter 505 and the color separator506 perform processing on all the pixels of the inputted decoded JPEGdata, a huge amount of calculation and a very large number of memoryaccesses are required. However, performing color process caching usingthe MCU data patterns which can be specified by the MCU classificationdata 520 allows a large amount of reduction in the processing and thenumber of memory accesses for the color conversion to be realized.

The processing in the color separated data generator 504 of the presentexemplary embodiment will be hereinafter explained with reference toFIG. 8 to FIG. 12.

FIG. 8 is a flow chart describing processing executed by the colorseparated data generator 504 of the first exemplary embodiment of thepresent invention. The drawing shows processing in a case that decodeddata for a given MCU and the MCU classification data 520 for the MCU areinputted to the color separated data generator 504. Note that theprogram for executing this processing is stored in the memory 1014, andis executed under the control of the CPU 1001 a.

First, in step S11, the color separated data generator 504 judgeswhether the inputted MCU classification data 520 for the MCU is “1”,i.e. the above described “pattern A”. If the MCU classification data 520is “1”, then the process advances to step S12, and executes colorseparated data generation processing 1 corresponding to “pattern A”.Note that the “color separated data generation processing 1” in step S12is described in detail later with reference to the flowchart of FIG. 9.

In a case that, in step S11, the MCU classification data 520 is not “1”the process advances to step S13, and determines whether the MCUclassification data 520 is “2”, i.e. the above-described “pattern B”. Ifthe MCU classification data 520 is “2”, then the process advances tostep S14 and executes color separated data generation processing 2 whichmakes use of the properties of pattern B. The “color separated datageneration processing 2” of step S14 is described in detail later withreference to the flowchart of FIG. 10.

In a case that, in step S13, the MCU classification data 520 is not “2”,the process advances to step S15, and determines whether the MCUclassification data 520 is “3”, i.e. the above-described “pattern C”. Ifthe MCU classification data 520 is “3”, then the process advances tostep S16 and executes color separated data generation processing 3 whichmakes use of the properties of pattern C. The “color separated datageneration processing 3” of step S16 is described in detail later withreference to the flowchart of FIG. 11.

In a case that, in step S15, the MCU classification data 520 is not “3”,it is understood that the MCU is of “pattern D”, and the processadvances to step S17 and executes color separated data generationprocessing 4 which takes into account the properties of pattern D. The“color separated data generation processing 4” of step S17 is describedin detail later with reference to the flowchart of FIG. 12.

The flowchart of FIG. 8 describes the processing in the color separateddata generator 504 to switch between the color separated data generationprocessing in accordance with the MCU classification data 520.

The processing of the “color separated data generation processing 1”will be explained with reference to FIG. 9.

FIG. 9 is a flowchart describing the color separated data generationprocessing 1 of step S12 in FIG. 8, corresponding to an MCU of “patternA”. In “pattern A”, 8×8 pixels in the MCU all have the same pixel value.Hence, in this processing, color space conversion and color separationprocessing are executed on a single pixel in the MCU, and the result isapplied to all other pixels in the MCU, thereby realizing an increase inprocessing speed.

First, in step S21, a conversion flag is initialized to “0”. Note thatthe conversion flag is stored in the memory 1014. Then, the processadvances to step S22, and it is determined whether the MCUclassification data 520 for the immediately preceding MCU of a currentMCU is “1”. If so, the process advances to step S23, and the top-leftpixel values of the current MCU and the immediately preceding MCU arecompared, and it is determined whether or not the top-left pixel valuesare same. If the two top-left pixel values match, the process advancesto step S24, and the conversion flag is set to “1”, and the processproceeds to step S25. On the other hand, if it is determined in step S22that the MCU classification data 520 for the immediately preceding MCUis not “1”, or if it is determined in step S23 that the top-left pixelvalues of the current MCU and the immediately preceding MCU fail tomatch, the process advances to step S25.

In step S25, it is determined whether the value of the conversion flagis “0”. If the value is “0” (not match with the immediately precedingMCU), then pixel value calculation of the current MCU is necessary andso the process advances to step S26. In step S26, the above-describedcolor space conversion processing and color separation processing on thetop-left pixel of the current MCU are performed to generate colorseparated data. The process then advances to step S27, the colorseparated data obtained in step S26 are cached and then proceeds to stepS28. The processing up to and including step S27 allows the preparationof color processing cache data for outputting the color separated dataof the current MCU.

On the other hand, the conversion flag value of “1” in step S25indicates consecutive MCUs of “pattern A” and that the current MCU isthe same color as the immediately preceding MCU. Hence, the cached dataused when outputting the color separated data of the immediatelypreceding MCU, can be applied to the current MCU without alteration. Theprocess therefore skips the calculation processing of step S26 and stepS27, and advances to step S28.

In steps S28 and S29 (and steps S31 and S32), loop processes ofx-direction and y-direction pixels which allow the processing of stepS30 to be performed on all 8×8 pixels of the current MCU areimplemented. Thus, the processes of step S29 to step S31 result in theoutput of color separated data (cache data) in step S30 for the eightx-direction pixels (x=0 to x=7) indicated by a y-direction coordinatevalue. Then, by means of step S28 and step S32, the processes of stepsS29 to step S31 are executed for the eight pixel lines corresponding toy=0 to y=7. In this way, the color separated data used for theimmediately preceding MCUs or the color separation data cached in stepS26 and step S27 are outputted as pixel values of the current MCU.

According to the processing shown in FIG. 9, it is possible to reducethe number of executions of the color space conversion processing andthe color separation processing for the 8×8 set of 64 pixels by makinguse of the properties of “pattern A”. The reduced amount of operationsand fewer memory accesses of this processing allow fast color separationprocessing to be realized.

For the sake of convenience, a comparison of top-left pixels in the MCUswas described, but any corresponding pixels included in the MCUs may beused.

FIG. 10 is a flowchart describing the color separated data generationprocessing 2 of step S14 in FIG. 8 corresponding to an MCU of “patternB”. Since “pattern B” has sets of eight pixels in the y-direction columnwhich have the same value, color space conversion processing and colorseparation processing are executed on only one pixel in each y-directioncolumn. Each result is then applied to all other pixels in thecorresponding y-direction column, thereby speeding up the processing.

In steps S41 and S42 (and steps S47 and S48), loop process forx-direction and y-direction pixel data is performed. In other words, forthe 8×8 pixels of the current MCU, the processing for eight pixel datain y-direction column, i.e. for each column, is repeated eight times inthe x-direction.

In step S43, it is determined whether y=0 or not, i.e. whether a pixelis the first (top) pixel in the y-direction column. If it is determinedy=0 in step S43, it indicates that the color processing cache data foroutputting the color separated data of the eight y-direction pixels hasnot been prepared, and the process therefore advances to step S44. Instep S44, the above-described color space conversion processing andcolor separation processing on the top pixel data are performed togenerate color separated data of the top pixel data. The process thenproceeds to step S45, and the color separated data obtained in step S44is stored as color processing cache data of the y-direction column. Theprocess then advances to step S46, and outputs the color processingcache data cached in step S45 as the color separated data for the targetpixel in the y-direction column.

Since the value of y for the next pixel data in the y-direction columnis no longer “0” because the value of y is incremented in step S47, theprocess advances from step S43 to step S46, the color separated datacached in step S45 is read out as the pixel value of the next pixel datain the y-direction column. This processing is executed for y=0 to y=7and further repeated for x=0 to x=7 as shown in steps S41 and S48.

As described above, the processing shown in the flowchart of FIG. 10makes use of the properties of “pattern B” to reduce the number ofexecutions of the color space conversion processing and the colorseparation processing on the 8×8 pixels (64 pixels) to a total of eightcalculations, one calculation for each column. As a result, fast colorseparation processing with a reduced amount of operations and fewermemory accesses can be realized.

For the sake of convenience, the case in which the pixel values of theuppermost row of pixels are calculated is described. However, colorconversion process may be implemented on a pixel value extracted fromanother position. In this case, the result would be cached, and thenapplied to all other pixels in the y-direction set that includes thetarget pixel.

FIG. 11 is a flowchart describing the color separated data generationprocessing 3 of step S16 in FIG. 8 corresponding to an MCU of “patternC”. Since “pattern C” has sets of eight pixel values in the x-directionrow which have the same value, color space conversion processing andcolor separation processing are executed on only one pixel in eachx-direction row. Each result is then applied to all other pixels in thecorresponding x-direction row, thereby speeding up the processing. Sincethis processing can be realized by switching x and y in the processingof the flowchart in FIG. 10, the description below is brief.

In steps S51 and S52 (and steps S57 and S58), the loop process forx-direction and y-direction pixel data is performed. In other words, forthe8×8 pixel (64 pixels) of the current MCU, the processing for pixeldata in the x-direction row, i.e. each row, is repeated eight times inthe y-direction.

In step S53, it is determined whether or not x=0, i.e. whether the pixelis the first (top) pixel in the x-direction row. If x=0, then theprocess advances to step S54, the above-described color space conversionprocessing and color separation processing on the top pixel areperformed to generate color separated data of the top pixel. The processthen advances to step S55, and the color separated data obtained in stepS54 is cached as the color processing cache data for the x-directionrow. Then in step S56, the color processing cache data cached in stepS55 is read out as the color separated data for the target pixel in thex-direction row.

According to the processing shown in FIG. 11, it is possible to reducethe number of executions of the color space conversion processing andthe color separation processing for the 8×8 pixels (64 pixels) into atotal of eight calculations by making use of the properties of “patternC” and performing only one calculation for each x-direction row. As aresult, fast color separation processing resulting from fewercalculations for the pixels of the MCU and fewer memory accesses can berealized.

For the sake of convenience, the case in which the pixel value of theleftmost column of pixels (the first pixel in each row) is calculatedand the calculated value is applied to other pixels in the x-directionrow is described. However, the color conversion process may beimplemented on a pixel value extracted from another position in eachx-direction row. In this case, the result is cached and then applied toall other pixels in the x-direction row that includes the target pixel.

FIG. 12 is a flowchart describing the color separated data generationprocessing 4 of step S17 in FIG. 8 corresponding to an MCU of “patternC”. “Pattern D” differs from the above-described patterns in that thereis no guarantee of continuity of pixels in both the x-direction and they-direction. Hence, it is necessary to execute the color spaceconversion processing and the color separation processing on each of all8×8 pixels in the current MCU.

In steps S61 and S62 (and steps S65 and S66), the loop process forx-direction and y-direction pixel is implemented corresponding in numberto the number of pixels. In other words, the processes of step S63 tostep S64 are performed for each of 8×8 pixels in the current MCU. Instep S63, the color space conversion processing and color separationprocessing on the pixel is performed to generate color separated data ofthe pixel data. Then, in step S64, the color separated data obtained instep S63 is outputted as the color separated data for the pixel data.

With the above described processing in FIGS. 8 through 11, fast colorseparation processing that makes use of the DCT frequencycharacteristics of the MCU can be realized. Further, the processing ofFIG. 9, FIG. 10, and FIG. 11 has the following advantages in common.

As is clear from the above description, the processing of FIG. 9, FIG.10 and FIG. 11 can be realized with a construction which always stores asingle item of color processing cache data. Hence the cache region isreduced to a minimum, and the technique can be realized at lower coststhan techniques in which a plurality of items of color processing cachedata are generated and stored in a cache data table. Moreover, it isunnecessary to determine whether or not the color processing cache datashould be applied. This is because the data pattern of the MCU isspecified (as pattern A, B, C, or D) by the MCU classification data 520,and, for each data pattern, it possible to specify how the colorprocessing cache data should be generated and to which pixel thegenerated color processing cache data should be applied. As a result, iteliminates the judgment processing to determine whether or not the colorprocessing cache data is hit, and a further increase in the speed ofprocessing can be achieved.

Moreover, since the processing is performed with the MCU as the basicunit, the number of cache mishits generated between the MCUs can bereduced compared with the simple raster unit processing system. Thisarrangement has the advantage that the number of generation process ofcolor processing cache data can be reduced to a minimum.

The description of an arrangement in which the above-described fastgeneration processing for color separated data is applied in print datageneration processing will be explained.

As described above with reference to FIG. 4, print data is generated inaccordance with the following steps.

(1) An image file specified for printing is read and image data of theimage file decoded.

(2) The color space of the image data resulting from the decoding isconverted to a device-specified color space.

(3) The image data is resized in accordance with layout information.

(4) A conversion (half-toning) is performed to give quantized amountsrepresenting the state of each pixel.

Steps (1) and (2) of the above steps are realized by fast processingusing the above described arrangement. The following descriptionexplains how the remaining step (3) and step (4) are realized on thebasis of the above-described first exemplary embodiment.

Hereinafter, an arrangement in which the above-described generationprocessing for color separated data is applied in print data generationprocessing is described with reference to FIG. 13.

FIG. 13 is a block diagram explaining another example of color spaceconversion processing of the first exemplary embodiment of the presentinvention. The arrangement in FIG. 13 is the same as the arranging inthe above-described FIG. 5 from the Huffman decoder 500 to the colorseparated data generator 504, and the processing performed by each blockis the same as those in FIG. 5.

The scaling unit 507 resizes the color separated data outputted by thecolor separated data generator 504 to an actual print size in accordancewith layout information such as the paper size specified by the user andthe layout method. Various methods exist for resizing image data,including a nearest neighbor method, a bilinear method, and a bicubicmethod. Any of these methods may be used. Note, however, that in thecase of the bilinear and bicubic methods, since interpolationcalculations of plural pixel values are performed, it is difficult toprocess the image data in MCU units. It is necessary to input a band ofimage data composed of at least one line of MCUs to the scaling unit507. On the other hand, in a case that a scaling method, such as thenearest neighbor method, which does not require an interpolationcalculation using a plurality of items of pixel data is used, there isno particular limit on the input data units. Image data of single MCU,or of a band unit composed of a line of MCUs or the like can be receivedand processed.

A half-toning unit 508 implements a half-toning method, such as an errordiffusion method, on the color separated data that has been resized toan actual print size generated by the scaling unit 507, and quantizesand outputs the result. For instance, in a case that the error diffusionmethod is used as the half-toning method, the properties of theprocessing for diffusing the error in the error diffusion methodrequests for the scaling unit 507 to prepare at least image data of oneraster. Hence, it is necessary to prepare a band of resized image datagenerated from at least one MCU line, and input the resized image datato the half-toning unit 508.

With the above-described arrangement, it is possible to realize printdata generation processing using fast color separated data generationprocessing that makes use of the frequency characteristics in MCU.

Second Exemplary Embodiment

In the first embodiment above, an example of the processing forgenerating the color separated data from the decoded JPEG data isaccelerated by making use of the MCU frequency characteristics isdescribed. However, if a scaling method in the scaling unit 507, such asthe nearest neighbor method in the first exemplary embodiment, whichdoes not necessitate interpolation calculations using pixel values froma plurality of pixels is used, then it is possible to accelerate thescaling processing as well as the color separation processing. This isbecause in scaling methods, such as the nearest neighbor method, whichdo not necessitate interpolation calculations using a plurality of pixelvalues, it possible to implement scaling processing in an MCU unit.

Thus, in the second exemplary embodiment, an example is described inwhich the scaling method is assumed to be one which does not necessitateinterpolation calculations using plural pixel values, the colorseparated data is speedily generated after scaling, and the print datais generated from the resized color separated data. Thus in thefollowing description, it is assumed that the nearest neighbor method isused as the scaling method in the scaling unit 507.

FIG. 14 is a block diagram explaining color space conversion processingof a second exemplary embodiment of the present invention.

In the drawing, the Huffman decoder 500, the inverse quantization unit501, the IDCT unit 502, the MCU classification data generator 503, thecolor space converter 505, the color separator 506, and the half-toningunit 508 are the equivalents of those shown in FIG. 5 and FIG. 13. Sincethe arrangement of FIG. 14 only differs from the above-described firstexemplary embodiment in terms of a resized color separated datagenerator 509 and a scaling unit 510, the description is limited tothese two units.

The resized color separated data generator 509 receives the decoded JPEGdata and the MCU classification data 520, and rapidly generates colorseparated data resized to the actual print size determined by theuser-specified layout information.

The following describes details of the processing performed by theresized color separated data generator 509 and the scaling unit 510,with reference to flowcharts in FIG. 15 to FIG. 19.

FIG. 15 is a flow chart describing processing executed by the resizedcolor separated data generator 509 of the image processing apparatus ofthe second exemplary embodiment of the present invention. The drawingshows the processing performed in a case that decoded data of a givenMCU and MCU classification data 520 of the MCU are inputted to theresized color separated data generator 509. Since the construction ofthe image processing apparatus 12 of the second exemplary embodiment isthe same as the construction of the image processing apparatus of thefirst exemplary embodiment (FIG. 2), a description of the imageprocessing apparatus is omitted. Note that the program for executing theprocessing is stored in the memory 1014, and is executed under thecontrol of the CPU 1001 a.

First, in step S71, it is determined whether or not the MCUclassification data 520 of a current MCU is “1”. If it is determined instep S71 that the MCU classification data 520 is “1”, it is determinedthat the MCU is of “pattern A”, and the process advances to step S72 andresized color separated data generation processing 1 is executed asshown in FIG. 16 which takes into account the properties of pattern A.Note that the resized color separated data generation processing 1 isdescribed later with reference to the flowchart of FIG. 16.

If it is determined in step S71 that the MCU classification data 520 isnot “1”, the process advances to step S73, and it is determined whetheror not the MCU classification data 520 is “2”. If the MCU classificationdata 520 is “2”, then it is determined that the MCU is of “pattern B”and the process advances to step S74 and resized color separated datageneration processing 2 which makes use of the properties of pattern Bis executed. The resized color separated data generation processing 2 isdescribed later with reference to the flowchart of FIG. 17.

If it is determined in step S73 that the MCU classification data 520 isnot “2”, the process advances to step S75, and it is determined whetheror not the MCU classification data 520 is “2”. If the MCU classificationdata is “3”, then it is determined that the MCU is of “pattern C”, andthe process therefore advances to step S76 and resized color separateddata generation processing 3 which makes use of the properties ofpattern C is executed. The resized color separated data generationprocessing 3 is described later with reference to the flowchart of FIG.18.

If it is determined in step S75 that the MCU classification data 520 isnot “3”, then it is determined that the MCU is of “pattern D”, and theprocess advances to step S77 and resized color separated data generationprocessing 4 which takes into account the properties of pattern D isexecuted. The resized color separated data generation processing 4 isdescribed later with reference to the flowchart of FIG. 19. Thus, asshown in the flowchart of FIG. 15, the resized color separated datagenerator 509 switches the resized color separated data generationprocessing method in accordance with the MCU classification data 520.

The resized color separated data generation processing 1 of the secondexemplary embodiment of the present invention will be explained withreference to the flowchart of FIG. 16.

FIG. 16 is a flowchart describing generation processing 1 (step S72) ofresized color separated data corresponding to an MCU of “pattern A” ofthe second exemplary embodiment. In “pattern A”, 8×8 pixels in the MCUall have the same value. Hence, in this processing, color spaceconversion and color separation processing are executed on a singlepixel in the MCU and the result is applied to all other pixels in thecurrent MCU, thereby realizing an increase in processing speed.

FIG. 16 shows processing for the case that an 8×8 pixel MCU has beenresized to a size of W×H pixels. The W×H size which results from scalingcan be calculated using a scaling method, such as the nearest neighbormethod. Since such methods have no special content, a description of thescaling method has been omitted from the second exemplary embodiment.

First, in step S81, a conversion flag is initialized to “0” and storedin the memory 1014 (FIG. 2). The process then proceeds to step S82, andit is determined whether the value of the MCU classification data 520for an immediately preceding MCU of the current MCU is “1”. If the valueis “1”, then the process advances to step S83, the top left pixels ofthe current MCU and the immediately preceding MCU are compared, and itis determined whether or not there is a match. If the two top leftpixels match, the process advances to step S84, the conversion flag ischanged to “1” to indicate that the cached color separated data can beused, and the process advances to step S85. Note that, if in step S82,the MCU classification data 520 is not “1” for the immediately precedingMCU, or if in step S83 the top-left pixel values of the current MCU andthe immediately preceding MCU fail to match, the process advances tostep S85.

In step S85, it is determined whether or not the value of the conversionflag is “0”. Here, a flag value of “1” indicates consecutive MCUs of“pattern A” and that the current MCU and the immediately preceding MCUare of the same color. Hence, the process advances to step S88, and thecached data used when outputting the color separated data of theimmediately preceding MCU to the current MCU without alteration.Conversely, if the value of the flag is “0”, then the process advancesto step S86 and the conversion processing is executed to generate colorseparated data for the current MCU.

In step S86 and steps S87, processing for generating the cache data isexecuted. In step S86, the above-described color space conversionprocessing and color separation processing on the top-left pixel of thecurrent MCU is performed to generate color separated data. The processthen advances to step S87, and the color separated data obtained in stepS86 is cached. Thus, the processing of step S86 and step S87 allowscolor processing cache data to be calculated for the output of theresized color separated data for the current MCU.

In steps S88 and S89 (and steps S91 and S92), loop processes for thepixels in the y-direction and the x-direction are implemented so thatthe processing of step S90 is performed on all pixels in the H×W regionof the resized current MCU. Then, in step S90, the color processingcache data, which as been cached in advance or in step S87, is outputtedas the resized color separated data for the target pixel.

According to the processing shown in FIG. 16, it is possible to reducethe number of executions of the color space conversion processing andthe color separation processing for the 8×8 pixels in the MCU by makinguse of the properties of “pattern A”. This enables fast color separationprocessing with fewer calculations and memory accesses to be realized.

Furthermore, processing with fewer memory accesses than the processingin the first exemplary embodiment can be realized. This is because,rather than performing the scaling after first storing the colorseparated data for the 8×8 pixels in the memory 1014, the data cached instep S87 is outputted directly as the resized color separated data instep S90.

For the sake of convenience, the case in which the color separated datais of the top-left pixel has been described, but a pixel of any positionin the MCU may be used.

The following describes the resized color separated data generationprocessing 2 with reference to FIG. 17.

FIG. 17 is a flowchart describing generation processing 2 (step S74) forresized color separated data corresponding to the MCU of “pattern B”, ofthe second exemplary embodiment. Since “pattern B” has sets of eightpixel values in the y-direction of the input data which have the same,color space conversion processing and color separation processing areexecuted on only one pixel in each y-direction column. The results arethen applied to pixels in the resized x-direction rows and y-directioncolumns, thereby speeding up the processing. For instance, in a casethat the current MCU is resized to a 16×16 pixel set using the nearestneighbor method, a single item of color processing cache data is appliedto a 2×16 pixel region.

FIG. 17 is a flowchart showing the processing for a case that an 8×8pixel MCU has been resized to a W×H pixel set. The W×H size whichresults from scaling can be calculated using a scaling method, such asthe nearest neighbor method. Since such methods have no content relevantto this document, a description of the scaling method has been omittedfrom the second exemplary embodiment.

First, in step S101, a variable Sx is initialized to “0”. The variableSx is stored in the memory 1014. In step S102 and step S112, loopprocessing is performed for pixel of each x-direction row of the inputimage data. In step S103 and step S104, the color space conversionprocessing and the color separation processing are performed on a singlepixel at (x, 0) in each y-direction column of input image data, and theresults of the conversion are cached.

In step S105, the number of x-direction repetitions Wx for the outputcorresponding to the currently targeted input pixel data is calculated.Like the above-described W and H, Wx can be calculated using a nearestneighbor method without any content relevant to this application, and soa description of these calculations is omitted. Note that the total ofWx for x=0 to x=7 is W.

As a specific example of settings values, in a case that the MCU hasbeen resized to 16×16 using the nearest neighbor method, an item ofcolor processing cache data is applied to a 2×16 pixel region, and soWx=2 for all x.

In steps S106 and S107 (and steps S109 and S110), loop processing forx-direction and y-direction pixel data is performed to output resizeddata. In step S105, the color processing cache data obtained using theprocessing up to and including step S104 is outputted as the resizedcolor separated data to the Wx×H rectangular region with top-left pixelcoordinates (Sx, 0). In step S111, Wx is added to Sx to update theoutput position for the resized color separated data.

According to the processing shown in FIG. 17, it is possible to reducethe number of executions of the color space conversion processing andthe color separation processing for the 8×8 pixels into one pixel foreach column, and a total of eight calculations, by making use of theproperties of “pattern B”. As a result, fast color separation processingwith fewer calculations and memory accesses can be realized.

Furthermore, processing with fewer memory accesses than the processingin the above-described first exemplary embodiment can be realized. Thisis because, rather than performing the scaling after first outputtingthe color separated data for the 8×8 pixels to memory, the data cachedin step S104 is outputted directly as the resized color separated data.For the sake of convenience, the case in which calculations areperformed for the uppermost row of pixels is described. However, colorconversion may be implemented on pixels extracted from another position,and the result cached.

FIG. 18 is a flowchart describing generation processing 3 (step S76) forcolor separated data corresponding to the MCU of “pattern C”, of thesecond exemplary embodiment. Since “pattern C” has pixel values whichare the same for sets of eight pixels in the x-direction row of theinput image data, the color space conversion processing and colorseparation processing are executed on only one pixel in each x-directionrow. The results are then applied to pixels in the resized x-directionrows and y-direction columns, thereby speeding up the processing. Forinstance, when the current MCU is resized to a 16×16 pixel set using thenearest neighbor method, an item of color processing cache data isapplied to a 16×2 pixel region.

FIG. 18 shows a flowchart of processing for a case that an 8×8 pixel MCUhas been resized to W×H pixels. The W×H size which results from scalingcan be calculated using a scaling method, such as the nearest neighbormethod. Since this scaling method has no special content relevant tothis application, a description has been omitted.

First, in step S121, a variable “Sy” is initialized to “0”. The variableSy is then stored in the memory 1014. In step S122 and step S132, loopprocesses are applied to each y-direction pixel of the image data.According to step S123 and step S124, the color space conversionprocessing and color separation processing are performed on pixel dataof on pixel in each x-direction row of the input data, and the resultsof the conversion are cached.

In step S125, the number of y-direction repetitions Hy for the outputcorresponding to the currently targeted input pixel data is calculated.Like the above-described W and H, Hy can be calculated using a nearestneighbor scaling method. Note that the total Hy for y=1 to y=7 is H.

As a specific example of settings values, in a case that the MCU hasbeen resized to 16×16 pixels using the nearest neighbor method, an itemof color processing cache data is applied to a 16×2 pixel region. Hence,Hy=2 for all y.

In steps S126 and S127 (and steps S129 and S130), loop processescorresponding in number to the number of pixels in the y-direction andthe x-direction are executed to output resized data. In step S128, thecolor processing cache data obtained using the processing up to andincluding step S124 is outputted as resized color separated data to theW×Hy size rectangular region with top-left pixel coordinates (0, Sy). Instep S131, Hy is added to Sy to update the output position for theresized color separated data.

According to the processing shown in FIG. 18, it is possible to reducethe number of executions of the color space conversion processing andthe color separation processing for the 8×8 pixels to one per row ofpixels, i.e. a total of eight times, by making use of the properties of“pattern C”. As a result, fast color separation processing with fewercalculations and memory accesses can be realized.

Furthermore, processing with fewer memory accesses than the processingin the above-described first exemplary embodiment can be realized. Thisis because, rather than performing the scaling after first storing thecolor separated data for the 8×8 pixels in the memory 1014, the datacached in step S124 is outputted directly as the resized color separateddata.

For the sake of convenience, the case in which calculations areperformed for the leftmost column of pixels is described. However, colorconversion may be implemented on pixels extracted from another position,and the result cached.

The resized color separated data generation processing 4 (step S77) isexplained with reference to FIG. 19.

FIG. 19 is a flowchart describing generation processing 4 of colorseparated data corresponding to an MCU of “pattern D” of the secondexemplary embodiment. “Pattern D” differs from the other patterns inthat there is no guarantee of continuity in the pixel values in both thex- and y-directions. Hence, it is necessary to execute color spaceconversion processing and color separation processing on all 8×8 pixelsin the MCU, cache the results of the conversion, and take into accountthe scaling of each pixel when outputting.

FIG. 19 shows processing for the case when an 8×8 pixel MCU has beenresized to a size of W×H pixels. The W×H size which results from scalingcan be calculated using a scaling method such as the nearest neighbormethod. Since such methods have no special content relevant to thesecond exemplary embodiment, a description of the scaling method hasbeen omitted.

First, in step S141, a variable “Sx” is initialized to “0”. The variableSx corresponds to the variable of step S101 in the flowchart of FIG. 17.In step S142 and step S157, loop processing for the x-direction pixelsof the input image data is executed.

In step S143, the number of x-direction repetitions Wx for the output ofthe currently targeted pixel data is calculated. Like theabove-described W and H, Wx can be calculated using a nearest neighborscaling method. Note that the total of Wx for x=0 to x=7 is W.

The process then proceeds to step S144, and initializes a variable Sy to“0”. The variable Sy corresponds to the variable of step S121 in theflowchart of FIG. 18. In step S145 and step S155), loop processing forthe y-direction pixels of the input data is executed.

In step S146, the color space conversion processing and the colorseparation processing on the pixel data in position (x,y), which is theinput data, are performed. Then, in step S147, the result of theconversion in step S146 is cached. In step S148, the number ofy-direction repetitions Hy for the output of the currently targetedinput pixel data is calculated. Like the above-described W and H, Hy canbe calculated using a nearest neighbor scaling method. Note that thetotal Hy for y=0 to y=7 is H.

In steps S149 and S150 (and steps S152 and S153), loop processescorresponding in number to the number of pixels in the x-direction andthe y-direction of the resized output data are executed. In step S151,the color processing cache data obtained using the processing up to andincluding step S147 is, after scaling, outputted as resized colorseparated data to the Wx×Hy size rectangular region with top-left pixelcoordinates (Sx, Sy). Then, in step S154, Hy is added to Sy to updatethe output position in the y-direction for the resized color separateddata. Similarly, in step S156, Wx is added to Sx to update the outputposition in the x-direction for the resized color separated data.

As described above, according to the processing of FIG. 19, it ispossible to implement the processing in accordance with the propertiesof “pattern D”. As described above, the number of executions of thecolor space conversion processing and the color separation processingcannot be reduced due to the properties of “pattern D”. However, it ispossible to realize processing with fewer memory accesses than theprocessing in the first exemplary embodiment. This is because, ratherthan performing the scaling after first outputting the color separateddata for the 8×8 pixels to the memory 1014, the data cached in step S147is outputted directly as the resized color separated data.

With the above-described processing, fast generation of the resizedcolor separated data can be realized thanks to use of the DCT frequencycharacteristics of the MCU. Note also that the processes in FIG. 16 toFIG. 19 have the following advantages in common.

As is clear from the above description, the processes of FIG. 16 to FIG.19 are realized using an arrangement in which only one item of colorprocessing cache data is stored. This means that the size of the cacheregion can be minimized. As a result the technique can be realized atlower cost than techniques in which a plurality of items of colorprocessing cache data are generated and stored in a cache data table.

Moreover, it is unnecessary to judge whether the color processing cachedata should be applied. This is because the data pattern of the MCU isspecified (as pattern A, B, C, or D) by the MCU classification data 520.Thus, for each data pattern, it is possible to specify how the colorprocessing cache data should be generated and to which pixels thegenerated color processing cache data should be applied for each datapattern. As a result, the processing, necessary in conventionaltechniques, of judging whether color processing cache data is hitbecomes unnecessary. This leads to a further improvement in speed.

Moreover, since the processing is performed with the MCU as the basicunit, the number of cache mishits generated between MCUs for the simpleraster unit processing system can be reduced. This allows the number ofgeneration operations of color processing cache data to be minimized.

The above described exemplary embodiments describe a system in which ahost apparatus and the image processing apparatus are connected or asystem in which a memory card is directly connected to the imageprocessing apparatus. However, it goes without saying that the presentinvention can also be applied to systems constructed from a plurality ofdevices and to other systems which receive image data compressed usingthe DCT and generate print data from the inputted image data.

Further, it is to be understood that the object of the present inventionmay also be achieved by supplying a system or device with a storagemedium (or recording medium) on which is stored a software program codefor realizing the functions of the above-described exemplaryembodiments. In this case, the object is achieved by the computer (orCPU, MPU or the like) of the device or system reading and executing theprogram code stored in the storage medium. It is then to be understoodthat the program code itself read from the storage medium realizes thefunctions of the above described embodiments and that the storage devicewith the program code stored thereon constitutes the present invention.Note that the functions of the above described exemplary embodimentsneed not be realized by the computer simply executing the read programcode. Rather, an operating system (OS) or the like running on thecomputer may perform a part or all of processing to realize thefunctions of the above described exemplary embodiments based oninstructions in the program code.

The functions of the above-described exemplary embodiment are alsorealized in cases such as the following. In such cases, the program coderead from the storage medium is written to a memory provided in afunction expansion card inserted into the computer or in a functionexpansion unit connected to the computer. The CPU provided with thefunction expansion card or function expansion unit then perform a partor all of the actual processing based on the instructions in the programcode.

In the above-described exemplary embodiments, the description is limitedto print data generation processing. However the present invention canbe applied in any technique in which some sort of conversion processing,such as conversion of pixel units to another color space, is implementedon image data, such as JPEG data, which has been compressed using theDCT. For instance, the present invention may be applied in colormatching processing or the like when displaying the JPEG images.

As described above, the exemplary embodiments allow a reduction in theamount of calculation and number of memory accesses in color processingon color image data compressed using the DCT, thereby enabling anincrease in processing speed.

Like the above-described Japanese Patent Laid-Open No. 2001-145107, inthe present exemplary embodiments, the processing load is reduced bypaying close attention to the properties of the DCT coefficients.However, whereas efficiency improvements offered by the Japanese PatentLaid-Open No. 2001-145107 are limited to MCUs of uniform color, thepresent exemplary embodiments further realize efficiency improvementsfor MCUs of non-uniform color.

Moreover, in the present exemplary embodiments, the color processingcaching can be realized at lower cost than in the techniques proposed inJapanese Patent Laid-Open No. 2005-53009. Only one group of calculationresults is ever cached so there is no need to generate a cache datatable. Hence, the size of the cache region can be reduced, and thepresent exemplary embodiments excel in terms of cost.

In the present exemplary embodiments, since MCUs are classified intodata patterns based on the DCT frequency properties, it is no longernecessary to search cache data tables and it is possible to realizefavorable processing without use of wasteful processes.

Moreover, since the processing is performed with attention to the MCUs,the number of cache mishits generated between MCUs can be reduced, andthe cache hit rate can be improved unlike the technique performing asimple rastering process.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims priority from Japanese Patent Application No.2006-336384, filed Dec. 13, 2006, which is hereby incorporated byreference herein in its entirety.

1. An image processing apparatus for processing compressed image datagenerated by segmenting image data into blocks and using a compressionmethod which applies a frequency transformation to each block, the imageprocessing apparatus comprising: a decoder configured to decode thecompressed image data and output decoded data; a block classificationunit configured to classify blocks according to frequency coefficientsin the blocks decoded by the decoder; and a color separated datagenerator configured to generate color separated data in block unitsbased on the decoded data decoded by the decoder and a result ofclassification by the block classification unit, wherein the blockclassification unit classifies the blocks as being at least one of (a) ablock A composed of only a DC component, (b) a block B composed only ofa DC component and horizontal frequency components, and (c) a block Ccomposed only of a DC component and vertical frequency components, andwherein the color separated data generator generates color separateddata for pixels of a single color in the block and outputs the generatedcolor separated data for all pixels in the block, for a block classifiedas being block A, the color separated data generator generates colorseparated data for a single stripe of pixels in the block and repeatedlyoutputs the generated color separated data in a column direction of thesame pixel value of the block, for a block classified as being block B,and the color separated data generator generates color separated datafor a single stripe of pixels in the block and repeatedly outputs thegenerated color separated data in a row direction of the same pixelvalue of the block, for a block classified as being block C.
 2. Theimage processing apparatus according to claim 1, wherein the colorseparated data generator uses the color separated data of an immediatelypreceding block of a current block, in a case that the current block andthe immediately preceding block are classified as being block A.
 3. Theimage processing apparatus according to claim 1, further comprising: aquantization unit configured to perform quantization on the colorseparated data to generate print data.
 4. The image processing apparatusaccording to claim 1, wherein the compressed image is a JPEG image andthe block is an MCU (Minimum Coded Unit).
 5. The image processingapparatus according to claim 4, wherein the decoder includes a Huffmandecoder, an inverse quantization unit, and an inverse frequencytransformation unit.
 6. The image processing apparatus according toclaim 1, wherein the color separated data generator includes: a colorspace converter configured to convert the decoded data to a predefinedcolor space; and a color separator configured to perform device-specificcolor separation on color space conversion data generated by the colorspace converter.
 7. The image processing apparatus according to claim 1,wherein the color separated data generator further includes a scalingunit configured to scale the color separated data.
 8. The imageprocessing apparatus according to claim 1, further comprising a scalingunit configured to resize the color separated data.
 9. An imageprocessing method for processing input compressed image data generatedby segmenting image data into blocks and using a compression method toapply a frequency transformation to each block, the image processingmethod comprising the steps of: decoding the compressed image andoutputting decoded data; classifying blocks according to frequencycoefficients in the blocks decoded in the decoding step; and generatingcolor separated data in block units based on the decoded data and aresult of classification in the classifying step, wherein, in theclassifying step, blocks are at least classified as being one of: (a) ablock A composed of only a DC component, (b) a block B composed only ofa DC component and horizontal frequency components, and (c) a block Ccomposed only of a DC component and vertical frequency components, andwherein, in the generating step, for a block classified as being blockA, color separated data for pixels of a single color in the block isgenerated and the generated color separated data for all pixels in theblock is output, in the generating step, for a block classified as beingblock B, color separated data for a single stripe of pixels in the blockis generated and the generated color separated data in a columndirection of the same pixel value of the block is repeatedly output, andin the generating step, for a block classified as being block C, colorseparated data for a single stripe of pixels in the block is generatedand the generated color separated data in a row direction of the samepixel value of the block is repeatedly output.
 10. The image processingmethod according to claim 9, wherein in a case that a current block andan immediately preceding block are classified as being block A, in thegenerating step, the color separated data of the immediately precedingblock of the current block is used.
 11. The image processing methodaccording to claim 9, further comprising the step of: performingquantization on the color separated data to generate print data.
 12. Theimage processing method according to claim 9, wherein the compressedimage is a JPEG image and the block is an MCU (Minimum Coded Unit). 13.The image processing method according to claim 12, wherein the decodingstep includes: a Huffman decoding step; an inverse quantization step;and an inverse frequency transformation step.
 14. The image processingmethod according to claim 9, wherein the generating step includes thesteps of: converting the decoded data to a predefined color space; andperforming device-specific color separation on color space conversiondata generated in the converting step.
 15. The image processing methodaccording to claim 9, wherein the generating step further includes astep of scaling the color separated data.